I have to say that MEnumerator.bas is truly a thing of beauty. Thank you for writing and releasing it!

As part of an SO answer, I adapted it slightly to use a named interface, and to support unlimited (?) item counts. Would you have any interest in hosting that version alongside the present one? If so, I'm happy to submit a PR of the linked code.

Private Function PtrAdd(ByVal Pointer As Long, ByVal Offset As Long) As Long
Const SIGN_BIT As Long = &H80000000
PtrAdd = (Pointer Xor SIGN_BIT) + Offset Xor SIGN_BIT
End Function

Can you please explain the use of this function? I don't see any functionality here. I tried it with huge pointer values where high bit is set. When I set a 32bit long in memory and set the bytes manually and I add 2 I get the same results like your code returns without additional XOr-ing

Dim pMem As Long

pMem = CoTaskMemAlloc(4)
MemByte(pMem) = 10
MemByte(pMem + 1) = 255
MemByte(pMem + 2) = 255
MemByte(pMem + 3) = 255

Debug.Print MemLong(pMem) 'it returns -246

'Add 2 to the low byte of long
MemByte(pMem) = 12

Debug.Print MemLong(pMem) 'it returns -244, which is in fact -246+2

Dim PtrAdd As Long

PtrAdd = (-246& Xor &H80000000) + 2& Xor &H80000000

Debug.Print PtrAdd  'returns as well -244